Embodiments of the invention generally relate to a control system of a rotary wing aircraft, and more particularly, to a system for independent speed and attitude control for a rotary wing aircraft.
A conventional helicopter controls aircraft speed with rotor tilt via attitude change. Hover attitude is fixed for a conventional helicopter and may not be optimal for visibility or air/ground transitions, such as slope landings. Maneuvering to change aircraft speed requires an attitude change that can also impact visibility and ride comfort in a conventional helicopter.
A hybrid helicopter, such as a rotary wing aircraft with a coaxial contra-rotating rotor system and a translational thrust system, can control aircraft speed and attitude independently. A translational thrust system can include an integrated propulsor unit with a propulsor (e.g., a propeller) oriented substantially horizontal and parallel to the aircraft longitudinal axis to provide supplemental thrust. Using the translational thrust system, aircraft speed can be held at a range of attitudes. This can allow a hybrid helicopter to hover at a variety of attitudes, maneuver at low speeds at a variety of attitudes, as well as transition to forward flight at a fixed pitch attitude. The ability to maintain pitch attitude or vary attitude independent of aircraft speed during changes in aircraft speed can provide additional time on target for military applications, and increased ride comfort for medevac and civil applications. This capability can also reduce hub loads during slope landings. Manual control of propulsor pitch in the translational thrust system can be provided using a beeper, which allows for control of an additional degree of freedom but significantly increases pilot workload. Manually coordinating aircraft attitude, position (i.e., hover position), speed, and/or altitude can be particularly challenging for a pilot when performing precision maneuvers.
Therefore, a need exists for an improved automatic control approach to independent speed and attitude control for a rotary wing aircraft.